Unit 1 – Part 2: The AtomObjective – learn about the theories of the atom and how they are applied.

Crash course, the history of chemistry: https://youtu.be/thnDxFdkzZs

Key Terms1. Dalton’s Atomic Theory

2. Modern Atomic theory

3. Electron (include size, mass and charge)

4. Nucleus

5. Proton (include size, mass and charge)

6. Neutron (include size, mass and charge)

7. Atomic number

8. Isotopes

9. Mass number

10. Atomic mass

Dalton’s Atomic Theory (OLD)

• All matter is composed of extremely small particles called atoms.

• Atoms cannot be subdivided, created, or destroyed.

• Atoms of a given element are identical in size, mass, and other properties.

• All matter is composed of atoms.

• Atoms of any one element differ in properties from atoms of another element.

• Atoms are divisible into even smaller particles.

• A given element can have atoms with different masses.

Modern Atomic Theory (NEW)

Subatomic particles

• An atom is the smallest particle of an element that retains the chemical properties of that element.

• Lets draw it!

Subatomic particles

• The nucleus is a small region at the center.

• It is made up of a positively charged particle called a proton and neutral particles called neutrons.

• Surrounding the nucleus is a region occupied by negatively charged particles called electrons.

Atomic number

• Atoms of different elements have different numbers of protons.

• Atoms of the same element all have the same number of protons.

• Atomic number (Z) = number of protons = number of electrons

Mass Number

• The mass number is the total number of protons and neutrons that make up the nucleus of an isotope.

• Number of protons + number of neutrons = mass number

• Mass number – atomic number = number of neutrons

How many protons, neutrons, and electrons are in each of the following atoms? •p.157 (class book) •P.141 (Modern Chem) •Atomic number (Z) = # protons = # electrons•Mass number – atomic number = # neutrons

1. Lithium and Boron2. Barium and Radon3. Sodium and Platinum4. Magnesium and Argon 5. Aluminum and Fluorine 6. Lead and Zinc7. Arsenic and Polonium 8. Nitrogen and Xenon9. Sulfur and Krypton 10. Silicon and Copper

Isotopes

• Isotopes are atoms of the same element that have different masses.• The isotopes of a particular element all have the same number of protons and

electrons but different numbers of neutrons.

• Hyphen notation: The mass number is written with a hyphen after the name of the element - Uranium-235

• Nuclear symbol: The superscript indicates the mass number and the subscript indicates the atomic number.

• Mass number − atomic number = number of neutrons

• The number of neutrons is found by subtracting the atomic number from the mass number.

• Example with Uranium-235:

• 235 (protons + neutrons) − 92 protons = 143 neutrons

• Sample Problem

•How many protons, electrons, and neutrons are there in an atom of chlorine-37?

• mass number = number of neutrons + number of protons

• Sample Problem

•How many protons, electrons, and neutrons are there in an atom of chlorine-37?

•mass number = number of neutrons + number of protons

•37 mass number− 17 protons = 20 neutrons

•An atom of chlorine-37 is made up of 17 electrons, 17 protons, and 20 neutrons.

Atomic Mass Unit

• The standard used by scientists to compare units of atomic mass is the carbon-12 atom, which has been arbitrarily assigned a mass of exactly 12 atomic mass units, or 12 amu.

• One atomic mass unit, or 1 amu, is exactly 1/12 the mass of a carbon-12 atom.

• The atomic mass of any atom is determined by comparing it with the mass of the carbon-12 atom.

Example Problem

Calculate the atomic mass of magnesium.

•The three Mg isotopes have masses and relative abundances of

•23.985 amu (78.99%)

•24.986 amu (10.00%)

•and 25.982 amu (11.01%)

(mass of iso #1) (abundance of iso #1) + (mass of iso #2) (abundance of iso #2) = avg mass of element

Example Problem

• Information about element X:

- Isotope 1

- Mass of 6.015 amu

- Percent abundance of 7.5%

- Isotope 2 (still element X)

- Mass of 7.016

- Percent abundance of 92.5%

•What element is element X?

(mass of iso #1) (abundance of iso #1) + (mass of iso #2) (abundance of iso #2) = avg mass of element

Problems

1. Find the Atomic mass of Carbon.• Carbon-12: mass of 12 and a percent abundance of 98.89

• Carbon-13: mass of 13.0034 and percent abundance of 1.110

2. Find the atomic mass of Nitrogen. • Nitrogen 14: mass of 14.003074 and percent abundance of 99.63

• Nitrogen 15: mass of 15.000108 and percent abundance of 0.37

3. Find the atomic mass of Silicon. • Silicon 28: mass of 27.976927 and percent abundance of 92.23

• Silicon 29: mass of 28.976495 and percent abundance of 4.67

• Silicon 30: mass of 29.973770 and percent abundance of 3.10